题解 | 找出每个学校GPA最低的同学

select
device_id,
a.university,
a.gpa
from user_profile a
join 
(select university, min(gpa) mingpa
 from user_profile c 
 group by university) b
 on a.university = b.university and a.gpa = b.mingpa
order by university

考查的就是子查询，可以用in，也可以用join,但我喜欢用join,join的性能会更好一点